Methods and devices for implementing time of day pacing adjustments

ABSTRACT

Methods and systems are directed to delivering cardiac pacing therapy to a patient. A pacing therapy associated with one or more pacing parameters is delivered. Alternate cardiac pacing therapies associated with one or more alternate pacing parameters are transitioned to, based on a sleep/wake cycle of the patient. Interactions between the pacing parameters of the pacing therapy and the alternate pacing parameters are resolved. Resolving pacing parameters may be based on analysis of lower rate limits and/or lower rate hysteresis.

FIELD OF THE INVENTION

The present invention relates generally to cardiac rhythm managementdevices and, more particularly, to delivering, with a cardiac rhythmmanagement device, cardiac pacing therapy with one or more cardiacpacing parameters adjusted in accordance with a patient's sleep/wakecycle.

BACKGROUND OF THE INVENTION

The healthy heart produces regular, synchronized contractions. Rhythmiccontractions of the heart are normally controlled by the sinoatrial (SA)node, specialized cells located in the upper right atrium. The SA nodeis the normal pacemaker of the heart, typically initiating 60-100 heartbeats per minute. When the SA node is pacing the heart normally, theheart is said to be in normal sinus rhythm (NSR).

If heart contractions are uncoordinated or irregular, the heart isdenoted to be arrhythmic. Cardiac arrhythmia impairs cardiac efficiencyand can be a potential life threatening event. Cardiac arrhythmias havea number of etiological sources including tissue damage due tomyocardial infarction, infection, or degradation of the heart's abilityto generate or synchronize the electrical impulses that coordinatecontractions.

Bradycardia occurs when the heart rhythm is too slow. This condition maybe caused, for example, by delayed impulses from the SA node, denotedsick sinus syndrome, or by a blockage of the electrical impulse betweenthe atria and ventricles. Bradycardia produces a heart rate that is tooslow to maintain adequate circulation.

When the heart rate is too rapid, the condition is denoted tachycardia.Tachycardia may have its origin in either the atria or the ventricles.Tachycardias occurring in the atria of the heart, for example, includeatrial fibrillation and atrial flutter. Both conditions arecharacterized by rapid, uncoordinated contractions of the atria.

Ventricular tachycardia occurs, for example, when a pulse is initiatedin the ventricular myocardium at a rate more rapid than the normal sinusrhythm. Ventricular tachycardia can quickly degenerate into ventricularfibrillation (VF). Ventricular fibrillation is a condition denoted byextremely rapid, nonsynchronous contractions of the ventricles. Therapid and erratic contractions of the ventricles cannot effectively pumpblood to the body and the condition is fatal unless the heart isreturned to sinus rhythm within a few minutes.

Implantable cardiac rhythm management systems have been used as aneffective treatment for patients with serious arrhythmias. These systemstypically comprise circuitry to sense signals from the heart and a pulsegenerator for providing electrical pulses to the heart. Leads extendinginto the patient's heart are connected to electrodes that contact themyocardium for sensing the heart's electrical signals and for deliveringpulses to the heart in accordance with various therapies for treatingthe arrhythmias described above.

Pacemakers may be incorporated into cardiac rhythm management systems todeliver pace pulses to the heart. Pace pulses are low energy electricalpulses timed to assist the heart in producing a contractile rhythm thatmaintains cardiac pumping efficiency. Pace pulses may be intermittent orcontinuous, depending on the needs of the patient. There exist a numberof categories of pacemaker devices, with various modes for sensing andpacing the heart. Single chamber pacemakers may pace and sense one heartchamber. A typical single chamber pacemaker is connected to a leadextending either to the right atrium or the right ventricle. Dualchamber pacemakers may pace and sense two chambers of the heart. Atypical dual chamber pacemaker is typically connected to two leads, onelead extending to the right atrium and one lead to the right ventricle.

Pacemakers may be used to provide pacing pulses to both the leftventricle and the right ventricle. This type therapy may be used, forexample, to coordinate ventricular contractions when a patient suffersfrom congestive heart failure (CHF). Congestive heart failure is acondition wherein the muscles of the heart deteriorate, causing theheart muscle to enlarge. Enlargement of the heart causes the contractileimpulses to travel more slowly, resulting in asynchronous contractionsof the left and right ventricles and reduced pumping efficiency.

Pacemakers can be programmed to provide pace pulses to the heart ondemand or at a fixed rate. When a pacemaker paces the heart at a fixedrate, the pacemaker provides pace pulses to the heart without takinginto account the heart's spontaneous action. In contrast, pacemakers maysense the spontaneous activity of the heart and provide pace pulsessynchronized to the spontaneous activity.

For example, a single chamber ventricular pacemaker may sense and pace aventricle. The pacemaker senses ventricular activity and provides a pacepulse to the ventricle if no spontaneous activity is sensed. If thepacemaker senses spontaneous activity, the pacing pulse is inhibited. Inthis example, where the pacemaker senses the ventricle, paces theventricle and inhibits the ventricular pace pulse upon sensing aspontaneous R-wave, the pacemaker mode is denoted VVI. Alternatively, asingle chamber pacemaker may sense and pace the atrium. In the casewhere the pacemaker senses the atrium, paces the atrium and inhibits theatrial pace pulse upon sensing a spontaneous P-wave, the pacemaker modeis denoted AAI.

A dual chamber pacemaker may be capable of sensing and pacing both theatrium and ventricle. The dual channel pacemaker is capable of usingpace pulses to synchronize atrial and ventricular activity. Ifspontaneous cardiac activity is detected in the atrium or the ventricle,pacing pulses may be triggered or inhibited. When the pacemaker pacesand senses both chambers and can trigger or inhibit pace pulses basedupon sensed signals, for example, the pacemaker mode is denoted DDD.Various other configurations involving providing or inhibiting pacepulses based upon sensed cardiac events using dual or single chamberpacemakers are known in the art.

Rate adaptive pacemakers provide pacing at rates responsive to thepatient's metabolic activity. Changes in metabolic activity may reflectexercise or non-exercise related changes, such as stress or excitement.The level of metabolic activity may be determined by sensing motion,respiratory rate, QT interval, venous oxygen saturation, temperature, orother patient conditions, for example. The pacemaker automaticallyadjusts the pacing rate to accommodate the sensed changes in thepatient's condition.

Implantable cardioverter/defibrillators (ICDs) have been used as aneffective treatment for patients with serious cardiac arrhythmias. Forexample, ICDs are capable of delivering high energy shocks to the heart,interrupting the ventricular tachyarrhythmia or ventricular fibrillationand allowing the heart to resume a normal rhythm. ICDs may includepacing functions described above as well as acardioversion/defibrillation capability.

SUMMARY OF THE INVENTION

Various embodiments of present invention involve methods and systems forimplementing time of day-based pacing parameter adjustments.

In one embodiment a method for delivering therapy to a patient requiresdelivering a cardiac pacing therapy associated with one or more pacingparameters. An alternate cardiac pacing therapy with one or morealternate pacing parameters is transitioned to based on a sleep/wakecycle of the patient. According to the embodiment, any interactionsbetween the pacing parameters of the pacing therapy and the alternatepacing parameters are resolved.

In various embodiments of the invention, resolving interactions betweenpacing parameters of pacing therapies includes using an alternate lowerrate limit associated with the alternate cardiac pacing therapy duringthe alternate pacing therapy if the alternate lower rate limit is belowa lower rate limit associated with the cardiac pacing therapy.

In other embodiments, resolving interactions between pacing parametersincludes using a lower rate hysteresis if the alternate lower rate limitassociated with the alternate cardiac pacing therapy is below the lowerrate limit associated with the cardiac pacing therapy.

In various other embodiments, resolving interactions between pacingparameters may include using a lower rate limit associated with thecardiac pacing therapy during the alternate cardiac pacing therapy if analternate lower rate limit associated with the alternate cardiac pacingtherapy is above the lower rate limit.

In another embodiment of the present invention, a cardiac rhythmmanagement system provides one or more electrodes for electricallycoupling to a heart, a pulse generator coupled to the one or moreelectrodes for delivering pacing pulses to the heart, circuitry foracquiring information associated with a patient's sleep/wake cycle, anda therapy controller coupled to the pulse generator and the sleep/wakecircuitry. The therapy controller controls transitions between aplurality of pacing therapies based on the patient's sleep/wake cycle.Pacing therapies include a pacing therapy associated with one or morepacing parameters and an alternate pacing therapy associated with one ormore alternate pacing parameters. The therapy controller additionallyincludes an arbitration processor configured to resolve interactionsbetween the pacing parameters of the pacing therapy and the alternatepacing parameters.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of a method for implementing sleep/wakecycle lower rate limit pacing adjustments in accordance with embodimentsof the invention;

FIG. 2 is a graph illustrating lower rate limits over a 24-hour periodof time in accordance with embodiments of the invention;

FIGS. 3A and 3B are transfer function graphs illustrating a lower ratelimit, lower rate hysteresis, and sensor rate hysteresis that may beutilized in transitioning from a pacing therapy to an alternate pacingtherapy in accordance with embodiments of the invention;

FIG. 4 is a flowchart of a method for adjusting pacing parametersaccording to a patient's sleep/wake cycle in accordance with embodimentsof the invention;

FIG. 5 is a partial view of a cardiac rhythm management (CRM) devicethat may be used to implement time of sleep/wake cycle pacing rateadjustments in accordance with embodiments of the invention; and

FIG. 6 is a block diagram of a cardiac rhythm management (CRM) devicesuitable for implementing sleep/wake cycle pacing rate adjustments inaccordance with embodiments of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings that form a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

When cardiac pacing therapy is delivered to a patient, the pacingtherapy is associated with various pacing parameters that controlvarious aspects of therapy delivery. The pacing parameters may beprogrammable and may include, for example, a lower rate limit (LRL)which is associated with a minimal pacing rate that the pacemaker willcontinuously pace at in the absence of intrinsic events. The LRLcorresponds to the longest escape interval that the pacemaker willcontinuously implement. Upon delivery of a pacing pulse, the pacemakerinitiates an escape interval. The escape interval is the period of timethat the pacemaker will delay before delivering the next scheduledpacing pulse. If an intrinsic event is sensed before expiration of theescape interval, the pacemaker inhibits the delivery of the scheduledpacing pulse and restarts the escape interval.

In addition to the LRL pacing constraint, the pacing rate delivered by apacemaker may be automatically adjusted based on information from ametabolic sensor that detects the patient's level of exertion orhemodynamic need. For example, when the metabolic sensor detects thatthe patient's level of activity has increased, the pacemakerautomatically increases the pacing rate. The pacing rate may beincreased, for example, from the LRL to a higher rate that correspondsto the patient's level of activity. The device continues to deliverpacing at the higher rate until the patient's activity level decreases,at which time the pacing rate is correspondingly lowered toward the LRL.

Human physiology is linked to a 24 hour clock known as the circadianrhythm. A number of biological processes modulate according to thisinternal clock. During sleep, the patient's metabolic functions slowdown, respiration becomes deeper, and heart rate slows. In one scenario,the pacemaker may mimic the patient's physiological response to sleep bytransitioning from a higher pacing rate to a lower pacing rate.

In some situations, slower pacing during sleep may not be desirable. Forexample, sleep may be linked to an increased likelihood of cardiacarrhythmia. Some patients are predisposed to nocturnal cardiac paroxysmsassociated with surges in vagal activity. A higher rate of pacing may beimplemented to prevent the occurrence of arrhythmia during sleep.Further, sleep may be associated with increased respiratory disruptions,such as sleep apnea. Studies have shown that overdrive pacing duringsleep may be an effective treatment for sleep apnea.

Embodiments of the invention involve transitioning between differentpacing therapies at different times of the day and in concert with thepatient's circadian rhythm. For example, FIG. 1 is a flowchartillustrating a method 100 for transitioning between different pacingtherapies. A primary pacing therapy associated with a first set ofparameters, including a primary lower rate limit, may be delivered 110when the patient is awake. The device may transition 120 to an alternatepacing therapy associated with a second set of pacing parameters,including an alternate lower rate limit, when the patient is asleep. Theprimary and/or alternate pacing therapies may involve rate adaptivepacing wherein the patient's pacing rate above a lower rate limit isdetermined based on sensed activity or hemodynamic need.

The device resolves 130 interactions between the pacing parameters ofthe primary therapy and those of the alternate therapy. Resolvinginteractions may include, for example, arbitrating between the primaryLRL and the alternate (LRL) used for rate adaptive pacing. Further,transitioning between primary and alternate pacing therapies may involveresolving interactions between additional pacing parameters, including,for example, lower rate hysteresis (LRH) and/or sensor rate hysteresis(SRH).

A hysteresis rate is an indication that the escape rate is a function ofthe history of the rate. For example, if the last event was a pacepulse, then the escape rate for the next cardiac cycle is equal to theprogrammed value of the lower rate. If the last event was a sensedintrinsic event, the escape rate is lower than the lower rate by apredetermined amount, e.g., 10 bpm. The rate hysteresis is oftenexpressed as a difference in quantity or a fixed quantity in pulses perminute. Lower rate hysteresis and/or sensor rate hysteresis areimplemented to allow the heart to beat via spontaneous, intrinsiccontractions rather than as a result of pacing.

In accordance with embodiments of the invention, the patient's pacingrate may transition back and forth between a primary pacing therapy andan alternate pacing therapy based on the patient's circadian rhythm orsleep/wake cycle. The patient's sleep/wake cycle may be determined byvarious methodologies. In one implementation, the pacemaker circuitrymay include a time of day clock. The patient's sleep and wake times maybe programmed during an initialization stage. For example, the pacemakermay be programmed during an initialization period with times thatcorrespond to implementation of the primary and/or alternate pacingtherapies. For example, the pacemaker may be programmed to implement theprimary (waking) therapy when the time of day clock indicates 7:00 a.m.and transition to the alternate pacing therapy when the time of dayclock indicates 11:00 p.m. each day.

In another implementation, the patient or physician may communicate inreal time with the pacemaker via a patient input device or other deviceto input information. Using such a device, the patient can indicate thathe or she is going to sleep or has awakened. Directly entering sleepinformation allows for increased flexibility in implementing the pacingtherapy transitions to correspond more closely to the patient's actualsleep/wake cycle.

In yet another implementation, the device may be equipped with sensorsand supporting circuitry for automatically identifying when the patientis asleep and when the patient wakes up. Detecting the patient'ssleep/wake cycle may be accomplished by examining transitions in heartrate, activity level, and/or respiration, for example. Methods andsystems for detecting sleep/wake cycles, aspects of which may beutilized in the embodiments described herein, are discussed in commonlyowned U.S. patent application Ser. No. 10/309,771, filed Dec. 4, 2000,now U.S. Pat. No. 7,189,204 and incorporated herein by reference.

In yet another implementation, pacing therapy transitions may be basedon certain events that occur during sleep. For example, a pacing therapytransition may occur when the patient's shifts to or from a particularsleep stage, such as a rapid eye movement (REM) sleep stage, a non-REMsleep stage, or a state of autonomic arousal. Detection of REM andnon-REM sleep stages is described in commonly owned U.S. patentapplication Ser. No. 10/643,006, filed Aug. 18, 2003, now U.S.Publication No. 2005/0043652 and incorporated herein by reference.Detection of autonomic arousal is described in commonly owned U.S.patent application Ser. No. 10/920,675, filed Aug. 17, 2004, now U.S.Publication No. 2005/0076908 and incorporated herein by reference. Insome implementations, as described in U.S. patent application Ser. No.10/643,006, the alternate pacing therapy may involve various diagnosticor test procedures that are performed which the patient is asleep toprovide diagnostic information about the patient or information aboutthe pacemaker functions.

In some embodiments, pacing therapy transitions may be triggered, forexample, when the device detects physiological parameters indicative ofsleep disordered breathing or other sleep related events. Methods andsystems for detection of sleep disordered breathing, aspects of whichmay be implemented in the embodiments of the present invention, aredescribed in commonly owned U.S. patent application Ser. No. 10/309,770,filed Dec. 4, 2002, now U.S. Pat. No. 7,252,640 and incorporated hereinby reference.

In some embodiments, the pacemaker may incorporate circuitry to morefully monitor the patient's sleep quality conditions during sleep. Forexample, the device may be equipped with circuitry to implement amedical event logbook and/or a sleep logbook that may track variousaspects of sleep quality and/or analyzes sleep-related events. In theseembodiments, pacing therapy transitions may be triggered based on thestate of the patient's sleep quality and/or other sleep related events,such as when the patient's disordered breathing corresponds to aparticular apnea/hypopnea index, for example. Methods and systems fortracking sleep quality and sleep related events are described in thefollowing commonly owned U.S. patent applications, all of which areincorporated herein by reference: Ser. No. 10/642,998, filed Aug. 18,2003; now U.S. Publication No. 2005/0042589; Ser. No. 11/012,430, filedDec. 15, 2004, now U.S. Publication No. 2006/0129193; and Ser. No.10/920,568, filed Aug. 17, 2004, now U.S. Publication No. 2005/0080348.

In an exemplary embodiment, the alternate pacing therapy involves adifferent LRL from the primary pacing therapy. Adjusting the pacing LRLbased on a patient's sleep/wake cycle can be beneficial to a patientbecause alternate pacing rates can be implemented at specific times ofthe day. Integrating an alternate sleep-time pacing lower rate limit,which is either greater than or less than a normal pacing lower ratelimit, can be advantageous for patients who benefit from a higher pacingrate for sleep apnea treatment, and/or a lower pacing rate during sleepto more closely mimic the patient's circadian or diurnal rhythm.

When the alternate sleep-time LRL is implemented by the pacemaker, thepacemaker transitions the pacing therapy to correspond with thesleep-time LRL parameter. For example, if the alternate sleep-time LRLis programmed to be activated at the patient's normal sleep time asindicated by a time of day clock, the alternate sleep-time LRL becomesactive at the appropriate time and the sensor rate and/or other ratedrivers are adjusted to account for the alternate sleep-time LRL. Whenthe patient's wake time occurs, as indicated by the time of day clock,the pacing rate is transitioned from the alternate (sleep-time) LRL tothe primary (wake-time) LRL. The transition period can be abrupt orgradual. During the time that the alternate LRL is active, the pacemakerarbitrates between competing parameters of the primary pacing therapyand the alternate pacing therapy as described herein.

FIG. 2 is a graph illustrating example LRLs that may be implemented overa 24-hour period of time. The primary lower rate limit 210 is active atleast during times of patient wakefulness. At a patient's bedtime, suchas at 8 PM, the lower rate limit 210 is transitioned to an alternatesleep-time lower rate limit. The alternate LRL may be higher 220 orlower 221 than the primary LRL 210.

As indicated in FIG. 2 the adjustment from the primary pacing therapyassociated with the primary LRL 210 to the alternate pacing therapyassociated with the alternate LRL occurs during a transition period 250.During the transition period the pacemaker may smoothly transition fromusing the primary wake-time lower rate limit 210 to the alternatesleep-time lower rate limit 220, 221 over a period of time, such asbetween about 5 minutes and about 2 hours with a preferred transitiontime of about 30 minutes. Thus, as illustrated by FIG. 2, at 8 p.m., theprimary LRL 210 is active. Between 8 PM and 8:30 PM the LRL 222 is in aperiod of gradual transition. At 8:30 PM the alternate LRL 220, 221 isactive.

The LRL of a pacing therapy may be associated with a lower ratehysteresis 230, illustrated in FIG. 2 and discussed further inconnection with FIGS. 3A and 3B. FIGS. 3A and 3B are transfer functiongraphs illustrating the pacing behavior of a dual chamber pacemakeroperating in DDDR mode. In this mode, the pacemaker is capable ofsensing and pacing both atrial and ventricular chambers. The pacemakermay trigger a pacing pulse or inhibit delivery of a scheduled pacingpulse based on sensed events. Further, the pacemaker operates in a rateresponsive pacing mode such that the pacing rate is controlled by ametabolic sensor. The rate responsive pacing rate may be subject to asensor hysteresis rate as described in connection with FIG. 3B.

FIG. 3A provides a diagrammatic representation of the transfer functionof a DDD pacemaker operating with a lower rate hysteresis. In FIG. 3A,the atrial sense (A-sense) rate is shown as the abscissa and theventricular sense (V-sense) rate is shown as the ordinate of the graph.In the atrial tracking range of operation of the pacemaker (point b topoint e ), there is 1:1 tracking between A-sense and a V-pace. That is,each A-sense is followed by a V-pace, one AV (atrial-ventricular) delayinterval later, i.e., operation is VDDx behavior. If the A-sense ratewere gradually reduced from point e until it was at point b, the V-paceswould track the A-senses 1:1 over this range. When the A-sense ratebecame lower than the hysteresis rate (point b), the pacemaker systemwould switch to an escape rate equal to the lower rate (point c). Therecan be one or more A-paces at the point b, which causes the switch tothe V-rate at point c. The operating behavior would now be DVI, that is,an A-pace followed by a V-pace at the lower rate.

As the A-sense rate is increased from point c, the escape rate wouldstay at the lower rate until the A-sense rate reached point d.Thereafter, the escape rate would follow the 1:1 curve, past the point dand up to point e.

The triangle defined by points b-c-d is referred to as the lower ratehysteresis loop. The length of the line b-c is usually expressed as aconstant value of rate (ΔHR). The length of the line could also beexpressed as a function of the rate or as a function of the interval,such as a percentage of the interval.

FIG. 3B further illustrates sensor rate hysteresis in DDDR Mode. If thesensor rate (SR) is less than the LRL, the pacemaker system would switchto an escape rate equal to the lower rate (point c). If the sensor value(SV) increases, the SR will then increase. This results in line g-kbeing located at a higher point in the graph as illustrated in FIG. 3B.In real terms, this indicates that the sensor rate can be much higherthan the A-pulse rate, and the actual demands of the patient may not bemet by the atrial function. If the A-sense rate was reduced from pointh, the V-rate will track the A-sense rate past point g and down to pointe. For A-sense rates below point e, the behavior of the pacemaker willswitch to point f. Pacing behavior will be DVIR with an escape rateequal to the SR. As the A-sense rate is reduced further, the operationof the pacemaker will follow line f-k. If the A-sense rate were toincrease, operation of the pacemaker would follow line k-g. For A-senserates above g, the operation of the pacemaker will follow line g-j.

Line e-f is the amount of sensor rate hysteresis. It is often expressedas a delta value of rate, but other values as described above for lowerrate hysteresis may also be used. The triangle described by e-f-g is thesensor rate hysteresis loop. Note that the lines k-g and c-f shift upand down with the sensor value. If the system is operating at point pand the sensor rate was reduced, operating behavior would remain as DVIRuntil the sensor rate reached point m. At point m, behavior would switchto VDDR, and as the SR continued to decrease, operation of the pacemakerwould follow line m-b. At point b, the operation of the pacemaker wouldswitch back up to point c. Pacemaker operation including hysteresisrates that may be utilized in embodiments of the invention is describedin commonly owned U.S. Pat. No. 5,891,175 which is incorporated hereinby reference.

As previously mentioned, transitioning from a primary therapy to analternate therapy in accordance with embodiments of the invention mayinvolve arbitrating between pacing parameters associated with theprimary therapy and the pacing parameters associated with the alternatepacing therapy. In some implementations, this involves arbitratingbetween a pacing rate indicated by the primary pacing therapy and apacing rate indicated by the alternate pacing therapy. For example, thelower pacing rate of the alternate therapy may be in conflict with alower rate hysteresis and/or a sensor rate hysteresis, requiringarbitration between the alternate LRL and the primary lower ratehysteresis or sensor rate hysteresis.

FIG. 4 is a flowchart of a method 400 for adjusting pacing parameters inconcert with a patient's sleep/wake cycle in accordance with embodimentsof the invention. As illustrated in FIG. 4, a wake-time therapy isdelivered 405 having parameter values for a sensor rate, a LRL, a lowerrate hysteresis and a sensor rate hysteresis, for example. The systemdetermines 410 if the patient is asleep. The sleep determination 410 canbe a result of an arbitrary patient sleep setting, e.g., where the sleepcycle is programmed to last from 11 p.m. to 7 a.m., or other timeperiod. Patient sleep can be detected using one or more sensorsindicative of patient activity or by using other methods.

If the patient is not asleep 420, wake time therapy continues to bedelivered 405 until sleep is detected. Once the determination is madethat the patient is asleep 415, the LRL of the pacing rate istransitioned 425 from a primary wake-time LRL to an alternate sleep-timeLRL. Transitioning between the primary LRL and the sleep-time lower ratelimit can be gradual or abrupt and can span a period from anywherebetween about five minutes to about two hours, with a preferabletransition period of 30 minutes. However, if the sensor pacing rate issignificantly above the LRL, the transition to the sleep-time LRL may bedelayed until the rate decreases.

During transition, adjustments may be made so that rate adaptive pacingutilizes the sleep-time LRL parameter. Accordingly, in the sleep-timemode, a determination 430 is made as to whether the alternate LRL ishigher than the primary LRL. If the alternate LRL is higher 435 than theprimary LRL, the pacemaker adjusts pacing so that the sensor rate isbased 445 on the primary LRL. The alternate LRL is arbitrated 450 withthe sensor indicated rate. Arbitration of the alternate LRL with thesensor indicated rate may involve, for example, delivering pacingtherapy to the patient at a rate corresponding to the greater of thealternate LRL and the sensor indicated rate. If the alternate LRL isgreater than the primary LRL 435, the pacemaker adjusts so that the LRLhysteresis is deactivated 455, but the sensor rate hysteresis remainsactive 460. In this scenario, the lower rate hysteresis would bedisabled because it is undesirable to lower the pacing rate when thealternate LRL is active and is higher than the primary LRL.

When the alternate LRL is not 440 higher than the primary LRL thepacemaker adjusts the rate adaptive pacing so that the sensor rate isbased 465 on the alternate LRL and the lower rate hysteresis remainsactive 470 so long as the alternate LRL is greater than the lower ratehysteresis.

Automatically resolving pacing parameter interactions during and/orafter transitioning from a primary pacing therapy to an alternate pacingtherapy is desirable for integrating a circadian or apnea therapy duringperiods of sleep into the patient's overall pacing regimen. Implementingalgorithms to automatically arbitrate between competing parametersprovides the desired pacing rate to the patient while reducing thedegree of complexity required for proper initialization of the pacingrate transitions.

FIG. 5 is a partial view of a cardiac rhythm management (CRM) devicethat may be used to implement pacing rate adjustments based onsleep/wake cycle in accordance with embodiments of the invention.Methods of the invention may be implemented in a variety of implantableor patient-external cardiac therapeutic and/or diagnostic devicesincluding, for example, pacemakers, pacemaker/defibrillators,bi-ventricular pacemakers, and/or cardiac resynchronization devices,among others. The CRM device illustrated in FIG. 5 includes animplantable housing 500 containing circuitry electrically coupled to anintracardiac lead system 502. Portions of the implantable housing may beconfigured as a can electrode 509. The housing 500 and the intracardiaclead system 502 is implanted in a human body with portions of theintracardiac lead system 502 inserted into a heart 501. The intracardiaclead system 502 is used to detect electric cardiac signals produced bythe heart 501 and to provide electrical energy to the heart 501 underpredetermined conditions to treat cardiac arrhythmias.

The intracardiac lead system 502 includes one or more electrodes usedfor pacing, sensing, and/or defibrillation. In the particular embodimentshown in FIG. 5, the intracardiac lead system 502 includes a rightventricular lead system 504, a right atrial lead system 505, and a leftventricular lead system 506. In one embodiment, the right ventricularlead system 504 is configured as an integrated bipolar pace/shock lead.

The right ventricular lead system 504 includes an SVC-coil 516, anRV-coil 514, and an RV-tip electrode 512. The RV-coil 514, which mayalternatively be configured as an RV-ring electrode 511 and an RV-coil514, is spaced apart from the RV-tip electrode 512, which is a pacingelectrode for the right ventricle.

The right atrial lead system 505 includes a RA-tip electrode 556 and anRA-ring electrode 554. The RA-tip 556 and RA-ring 554 electrodes mayprovide pacing pulses to the right atrium of the heart and may also beused to detect cardiac signals from the right atrium. In oneconfiguration, the right atrial lead system 505 is configured as aJ-lead.

In the configuration of FIG. 5, portions of the intracardiac lead system502 are shown positioned within the heart 501, with the rightventricular lead system 504 extending through the right atrium and intothe right ventricle. Typical locations for placement of the RV-tipelectrode 512 are at the right ventricular (RV) apex or the RV outflowtract.

In particular, the RV-tip electrode 512 and RV-coil electrode 514 arepositioned at appropriate locations within the right ventricle. TheSVC-coil 516 is positioned at an appropriate location within a majorvein leading to the right atrium chamber of the heart 501. The RV-coil514 and SVC-coil 516 depicted in FIG. 5 are defibrillation electrodes.

The left ventricular lead system 506 is advanced through the superiorvena cava (SVC), the right atrium 520, the ostium of the coronary sinus,and the coronary sinus 550. The left ventricular lead system 506 isguided through the coronary sinus 550 to a coronary vein of the leftventricle 524. This vein is used as an access pathway for leads to reachthe surfaces of the left atrium and the left ventricle which are notdirectly accessible from the right side of the heart. Lead placement forthe left ventricular lead system may be achieved via subclavian veinaccess and a preformed guiding catheter for insertion of the leftventricular (LV) electrodes 513 and 517 adjacent the left ventricle. Inone configuration, the left ventricular lead system 506 is implementedas a single-pass lead.

An LV distal electrode 513, and an LV proximal electrode 517 may bepositioned adjacent to the left ventricle. The LV proximal electrode 517is spaced apart from the LV distal electrode, 513 which is a pacingelectrode for the left ventricle. The LV distal 513 and LV proximal 517electrodes may also be used for sensing the left ventricle.

The lead configurations illustrated in FIG. 5 represent one illustrativeexample. Additional lead/electrode configurations may include additionaland/or alternative intracardiac electrodes and/or epicardial electrodes.For example, in one configuration, an extracardiac lead may be used toposition epicardial electrodes adjacent the left atrium for deliveringelectrical stimulation to the left atrium and/or sensing electricalactivity of the left atrium.

Referring now to FIG. 6, there is shown a block diagram of a cardiacrhythm management (CRM) device 600 suitable for implementing sleep/wakecycle pacing rate adjustments in accordance with embodiments of theinvention. FIG. 6 shows a CRM device 600 divided into functional blocks.It is understood by those skilled in the art that there exist manypossible configurations in which these functional blocks can bearranged. The example depicted in FIG. 6 is one possible functionalarrangement. Various functions of the CRM device 600 may be accomplishedby hardware, software, or a combination of hardware and software.

The CRM device 600 includes components for sensing cardiac signals froma heart and delivering therapy, e.g., pacing pulses or defibrillationshocks, to the heart. The circuitry of the CRM device 600 may be encasedand hermetically sealed in a housing 601 suitable for implanting in ahuman body. Power to the circuitry is supplied by an electrochemicalbattery power supply 680 that is enclosed within the housing 601. Aconnector block with lead terminals (not shown) is additionally attachedto housing 601 to allow for the physical and electrical attachment ofthe intracardiac lead system conductors to the encased circuitry of theCRM device 600.

In one embodiment, the CRM device 600 comprises programmablemicroprocessor-based circuitry, including control circuitry 620, amemory circuit 670, sensing circuitry 631, 632, 635, 636, and apacing/defibrillation pulse generator 641. Components of the CRM device600 cooperatively perform operations involving time of day pacingadjustments according to the approaches of the present invention. Thecontrol circuitry 620 may include a clock or a sleep processor 623 forimplementing time of day therapy control.

A clock may be utilized for determining the sleep/wake cycle based onprogrammed sleep times and wake times, for example. Alternatively, oradditionally, the sleep processor may acquire additional informationassociated with patient sleep. For example, the sleep processor maycomprise a sleep detector configured to sense that the patient is asleepand sense that the patient is awake. In another configuration, the sleepprocessor may include additional circuitry and sensors to detect sleepstages, sleep disturbances, such as disordered breathing, and sleepquality.

A therapy controller 622 includes circuitry that controls the transitionfrom a primary pacing therapy to an alternate pacing therapy. Furtherthe therapy controller 622 includes arbitration circuitry forarbitrating between conflicting therapy parameters.

The control circuitry 620 may encompass various functional components,for example, an arrhythmia classification processor 621 for detectingcardiac conditions such as bradycardia and a therapy control unit 622for controlling pacing therapy and arbitrating between pacing therapies.

The memory circuit 670 may store program instructions used to implementthe functions of the CRM device 600 as well as data acquired by the CRMdevice 600. For example, the memory circuit 670 may store historicalrecords of sensed cardiac signals, including arrhythmic episodes, and/orinformation about therapy delivered to the patient. The memory circuit670 may also store historical patient sleep-time information, parameteradjustment information including rate adjustment transition data.

The historical data stored in the memory 670 may be used for variouspurposes, including diagnosis of patient diseases or disorders. Analysisof the historical data may be used to adjust the operations of the CRMdevice 600. Data stored in the memory 670 may be transmitted to anexternal programmer unit 690 or other computing device, such as anadvanced patient management system as needed or desired.

Telemetry circuitry 660 allows the CRM device 600 to communicate with anexternal programmer unit 690 and/or other remote devices. In oneembodiment, the telemetry circuitry 660 and the external programmer unit690 use a wire loop antenna and a radio frequency telemetric link toreceive and transmit signals. In this manner, programming commands anddata may be transferred between the CRM device 600 and the externalprogrammer 690 after implant.

The CRM device 600 may function as a pacemaker and/or a defibrillator.As a pacemaker, the CRM device 600 delivers a series of electricalstimulations to the heart to regulate heart rhythm. Therapy controlcircuitry 622 controls the delivery of pacing pulses to treat variousarrhythmic conditions of the heart, for example. In various embodiments,the CRM device 600 may deliver pacing pulses to one or more of the rightatrium, left atrium, right ventricle and the left ventricle. The heartmay be paced to treat bradycardia, or to synchronize and/or coordinatecontractions of the right and left ventricles.

For example, right ventricular pacing may be implemented using unipolaror bipolar configurations. Unipolar RV pacing involves, for example,pacing pulses delivered between the RV-tip 512 to can 509 electrodes.Bipolar pacing involves, for example, delivery of pacing pulses betweenthe RV-tip 512 to RV-coil 514 electrodes. If an RV-ring electrode 511 ispresent, bipolar pacing may be accomplished by delivering the pacingpulses to the RV-tip 512 and RV-ring 511 electrodes.

Left ventricular pacing may be implemented using unipolar or bipolarconfigurations. Unipolar LV pacing may include, for example, pacingpulses delivered between the LV distal electrode 513 and the can 509.Alternatively, bipolar LV pacing may be accomplished by delivering thepacing pulses using the LV distal electrode 513 and the LV proximalelectrode 517.

Similarly, unipolar (RA-tip electrode 556 to can electrode 509) atrialpacing or bipolar (RA-tip electrode 556 to RA-ring electrode 554) atrialpacing may be provided by the CRM device 600.

In accordance with the present invention, the therapy controller 622 maybe programmed to adjust pacing parameters when pacing one or more of theright atrium, left atrium, right ventricle and the left ventricle basedon a patient's sleep/wake cycle. Furthermore, the therapy controllercircuitry 622, in accordance with the present invention, may adjust thepacing based on the sleep-time information acquired from the clock orsleep detector 623. For example, the therapy control circuitry 622 canarbitrate among competing parameters of a primary therapy and analternate therapy. The therapy controller 622 can implement gradual orabrupt transitions between a primary pacing therapy and an alternate,sleep-time pacing therapy, for example.

The CRM device 600 may also provide tachyarrhythmia therapy. Forexample, tachyarrhythmia therapy may be provided in the form ofanti-tachycardia pacing (ATP) pulses delivered to the heart. The ATPpulses may involve a series of timed paces of programmable width andamplitude that are implemented to interrupt a tachyarrhythmia episode.The ATP therapy may involve, for example, burst pacing at about 25 Hz toabout 50 Hz. In various implementations, the pace-to-pace interval mayhave a variable or constant length. For immediately life threateningarrhythmias, such as ventricular fibrillation, the therapy controlcircuitry 622 may control the delivery of one or a series ofdefibrillation shocks to the heart to terminate the fibrillation.

In the embodiment depicted in FIG. 6, electrodes RA-tip 556, RA-ring554, RV-tip 512, RV-ring 611, RV-coil 514, SVC coil 516, LV distalelectrode 513, LV proximal electrode 517, and can 509 are coupledthrough a switching matrix 610 to various sensing circuits 631, 632,635, 636. A right atrial sensing channel circuit 631 serves to sense andamplify electrical signals from the right atrium of the heart. Forexample, bipolar sensing in the right atrium may be implemented bysensing signals developed between the RA-tip 556 and RA-ring 554electrodes. The switch matrix 610 may be operated to couple the RA-tip556 and RA-ring 554 electrodes to the RA sensing channel circuit 631 toeffect bipolar sensing of right atrial signals. Alternatively, unipolarright atrial sensing may be accomplished by operating the switch matrix610 to couple the RA-tip 556 and can 509 electrodes to the RA sensingchannel circuit 631.

Cardiac signals sensed through the use of the RV-tip electrode 512 areright ventricular (RV) near-field signals and are referred to as RV ratechannel signals herein. Bipolar rate channel sensing may be accomplishedby operating the switch matrix 610 to couple the RV-tip 512, RV-ring 511and the RV-coil electrodes 514 through the RV rate channel sensingcircuitry 635. The rate channel signal may be detected, for example, asa voltage developed between the RV-tip 512 and the RV-coil 514electrodes. The RV rate channel sensing circuitry 635 serves to senseand amplify the RV rate channel signal.

Unipolar RV sensing may be implemented, for example, by coupling theRV-tip 512 and can 509 electrodes to the RV rate channel sensingcircuitry 635. In this configuration, the rate channel signal isdetected as a voltage developed between the RV-tip 512 to can 509sensing vector.

The RV lead system may also include an RV-ring electrode (not shown inFIG. 6) used for bipolar pacing and sensing. If an RV-ring electrode isincluded in the lead system, bipolar sensing may be accomplished bysensing a voltage developed between the RV-tip 512 and RV-ring (notshown) electrodes.

Far-field signals, such as cardiac signals sensed through use of one ofthe defibrillation coils or electrodes 514, 516 and the can 509, orusing both of the defibrillation coils or electrodes 514, 516, arereferred to as morphology or shock channel signals herein. The shockchannel signal may be detected as a voltage developed between theRV-coil 514 to the can electrode 509, the RV-coil 514 to the SVC-coil516, or the RV-coil 514 to the can electrode 509 shorted to the SVC-coil516. The switch matrix 610 is operated to couple the desired shockchannel sensing vector, e.g., RV-coil to can, to the right ventricularshock channel sensing circuitry 632. The RV shock channel sensingcircuitry 632 serves to sense and amplify the shock channel signal.

The outputs of the switching matrix 610 may also be operated to coupleselected combinations of the electrodes to LV sensing channel circuitry636 for sensing electrical activity of the left ventricle. Bipolar leftventricular sensing may be accomplished by operating the switch matrix610 to couple the LV-distal 513 and the LV proximal electrodes 517through the LV channel sensing circuitry 636. In this configuration, theLV signal is detected as a voltage developed between the LV proximal andLV distal electrodes.

Unipolar LV sensing may be implemented, for example, by coupling the LVdistal 513 and can 509 electrodes to the LV sensing circuitry 636. Inthis configuration, the LV signal is detected as a voltage developedbetween the RV-tip 512 to can 509 sensing vector.

The CRM device 600 may incorporate one or more metabolic sensors 645 forsensing the activity and/or hemodynamic need of the patient.Rate-adaptive pacemakers typically utilize metabolic sensors to adaptthe pacing rate to match the patient's hemodynamic need. A rate-adaptivepacing system may use an activity or respiration sensor to determine anappropriate pacing rate. Patient activity may be sensed, for example,using an accelerometer disposed within the housing of the pulsegenerator. Transthoracic impedance, which may be measured, for example,via the intracardiac electrodes, may be used to determine respirationrate. Sensor information from the metabolic sensor is used to adjust thepacing rate to support the patient's hemodynamic need. If the sensorsindicate the patient's activity and/or respiration rate is high, thenthe patient's pacing rate is increased above a lower rate limit tocorrespond to the level of activity or rate of respiration.

It will, of course, be understood that various modifications andadditions can be made to the preferred embodiments discussed hereinabovewithout departing from the scope of the present invention. Accordingly,the scope of the present invention should not be limited by theparticular embodiments described above, but should be defined only bythe claims set forth below and equivalents thereof.

1. A method for delivering cardiac pacing therapy to a patient,comprising: delivering a primary cardiac pacing therapy associated withone or more primary pacing parameters, including a primary lower ratelimit, and a sensor indicated pacing rate that is based on the primarylower rate limit; transitioning to an alternate cardiac pacing therapyassociated with one or more alternate pacing parameters, including analternate lower rate limit, the transition based on a sleep/wake cycleof the patient; and during delivery of the alternate cardiac pacingtherapy, in response to the alternate lower rate limit being greaterthan the primary lower rate limit, resolving interactions between theprimary pacing parameters of the primary pacing therapy and thealternate pacing parameters by selecting between pacing using thealternate pacing parameters and pacing using the sensor indicated ratewhich is based on the primary pacing parameters, the selecting based ona value of an alternate cardiac pacing parameter and a value of thesensor indicated rate.
 2. The method of claim 1, wherein delivering thecardiac pacing therapy comprises delivering a rate adaptive pacingtherapy using rate hysteresis; and selecting between pacing using thealternate pacing parameters and pacing using the sensor indicated ratecomprises selecting between maintaining activation or deactivating therate hysteresis.
 3. The method of claim 1, wherein transitioning to thealternate cardiac pacing therapy is initiated by input from an externalsource.
 4. The method of claim 1, wherein transitioning to the alternatecardiac pacing therapy comprises: detecting a change in a sleep/wakestatus of the patient; and transitioning to the alternate cardiac pacingtherapy based on the change in the patient's sleep/wake status.
 5. Themethod of claim 1, wherein selecting between pacing using the alternatepacing parameters and pacing using the sensor indicated rate that isbased on the primary pacing parameters comprises using an alternatelower rate limit associated with the alternate cardiac pacing therapyduring the alternate pacing therapy if the alternate lower rate limit isbelow a lower rate limit associated with the cardiac pacing therapy. 6.The method of claim 5, wherein resolving the interactions comprisesusing a lower rate hysteresis if the alternate lower rate limitassociated with the alternate cardiac pacing therapy is below the lowerrate limit associated with the primary cardiac pacing therapy.
 7. Themethod of claim 1, wherein selecting between pacing using the alternatepacing parameters and pacing using the sensor indicated rate comprisesusing a lower rate limit associated with the primary cardiac pacingtherapy during the alternate cardiac pacing therapy if an alternatelower rate limit associated with the alternate cardiac pacing therapy isabove the lower rate limit.
 8. The method of claim 7, wherein resolvingthe interactions between the primary pacing parameters of the primarycardiac pacing therapy and the alternate pacing parameters comprisesdisabling a lower rate hysteresis if the alternate lower rate limit isabove the lower rate limit.
 9. The method of claim 1, wherein resolvingthe interactions between the pacing parameters of the cardiac pacingtherapy and the alternate pacing parameters comprises arbitratingbetween a pacing rate indicated by the alternate cardiac pacing therapyand a pacing rate indicated by the primary pacing therapy.
 10. Themethod of claim 9, wherein arbitrating between the therapy interactionscomprises arbitrating between a pacing rate indicated by the alternatecardiac pacing therapy and a lower rate hysteresis indicated by theprimary cardiac pacing therapy.
 11. The method of claim 9, whereinarbitrating between the therapy interactions comprises arbitratingbetween a pacing rate indicated by the alternate cardiac pacing therapyand a sensor rate hysteresis indicated by the primary cardiac pacingtherapy.